Petrographic Characteristics and Geochemistry of Volcanic Rocks in the Kyaukmyet Prospect, Monywa District, Central Myanmar

The Kyaukmyet prospect lies approximately 5 km ENE of the highsulfidation Kyisintaung copper-gold deposit, Monywa district, central Myanmar. Geologically, the research area is remarked by magmatic extrusion that occurred during the Late Oligocene to Middle Miocene of Magyigon Formation which led to the outcrops of volcanic rocks. Study detailed on petrographical and geochemical of the Kyaukmyet volcanic rocks has not been performed before the present work. The principal aim of this paper is to document the petrographical and geochemical characteristics of volcanic suite rocks exposed in the Kyaukmyet prospect. The results of this data have provided insight into the origin of the rocks and petrogenetic processes during evolution. Petrographically, all the studied volcanic rocks in the research area show that trachytic and porphyritic textures with phenocrysts of quartz, plagioclase, and K-feldspar which are embedded in a fine to medium grained groundmass. The accessory minerals of this rock consist of biotite, chlorite and opaque mineral.Geochemically, these volcanic rocks having calc-alkaline nature and classified as volcanic field (rhyolite) as well as volcanic arc setting. Based on the chondrite normalized spider diagram, LREE has enriched to HREE in this area which indicated negative Eu anomaly and subduction tectonic setting.

Archean Zircons with Omphacite Inclusions from Eclogites of the Belomorian Province, Fennoscandian Shield: The First Finding

Early Precambrian retrogressed eclogites are abundant in the central and northern parts of the Belomorian Province of the Fennoscandian Shield (Gridino + Keret and Salma + Kuru-Vaara study areas, respectively). Older and younger eclogites are recognized and their Archean and Paleoproterozoic ages are argued. Archean eclogites are intensely retrogressed and occur in amphibolite boudins in the tonalite-trondhjemite-granodiorite (TTG) gneiss matrix of the Archean Gridino eclogite-bearing mélange. Less retrogressed Paleoproterozoic eclogites form patches in mafic dikes and some amphibolite boudins; their Paleoproterozoic age is supported by U-Pb/SIMS data on zircons depleted in heavy rare earth elements (REE) with omphacite, garnet, and kyanite inclusions, and Sm-Nd and Lu-Hf mineral isochrons. Archean eclogites contain Archean heavy rare-earth elements (REE)-depleted zircons with garnet and zoisite inclusions and Archean garnets. No omphacite inclusions were found in these zircons, and this fact was considered as evidence against the existence of Archean eclogites. This study reports on the first finding of omphacite (23–25% Jd) inclusions in 2.68 Ga metamorphic zircons from eclogites from the Gridino eclogite-bearing mélange. The zircons are poorly enriched in heavy REE and display a weak negative Eu-anomaly but a poor positive Ce-anomaly typical of eclogitic zircons. Thus, zircons with these decisive features provide evidence for an Archean eclogite-facies metamorphism.

The ‘europium anomaly’ in plants: facts and fiction

Rare earth elements (REEs) and normalized REE pattern determined in plant and soil samples represent powerful tools to trace biogeochemical processes during weathering, soil genesis and processes in the rhizosphere, and thus publications reporting rare earth elements and normalized REE pattern in soil systems and plants are increasing rapidly. Generally, a normalized REE pattern allow for the recognition of an anomalous concentrations of an individual REE. In the literature anomalies are predominantly reported/focused for/on the redox-sensitive elements cerium (Ce) and europium (Eu) that can shift their oxidation state during interactions with organic and inorganic soil phases and biological processes affecting the elements’ mobility in soil and uptake by plants. Thus positive Eu anomalies in plants are often interpreted as a consequence of reduction of Eu3+ to Eu2+ in the rhizosphere followed by a preferential uptake of Eu2+. However, due to an analytical artefact in ICP-MS analysis, a false Eu anomaly may be reported. This can be avoided by using a barium (Ba) interference correction. We draw attention to the possibility of this problem and to being aware of potential occurrence when Eu anomalies are reported. Finally, we recommend (i) including information on how this potential problem was dealt with in the Materials and Methods section of articles and (ii) how to implement FAIR principles in the section (including data availability on an open repository).

Strengths and limitations of in situ U-Pb titanite petrochronology in polymetamorphic rocks: An example from western Maine, USA.

Titanite is a potentially powerful U-Pb petrochronometer that may record metamorphism, metasomatism, and deformation. Titanite may also incorporate significant inherited Pb, the correction for which may introduce inaccuracies and result in geologically ambiguous U-Pb dates. Here we present laser ablation inductively coupled mass spectrometry (LA-ICP-MS)-derived titanite U-Pb dates and trace element concentrations for two banded calc-silicate gneisses from south-central Maine, USA (SSP18-1A & -1B). Single spot common Pb-corrected dates range from 400 to 280 Ma with 12–20 Ma propagated 2SE. Titanite in sample SSP18-1B exhibit regular core-to-rim variations in texture, composition, and date. We identify four titanite populations: 1) 399 ± 5 Ma (95 % CL) low Y + HREE cores and mottled grains, 2) 372 ± 7 Ma high Y + REE mantles and cores, 3) 342 ± 6 Ma cores with high Y + REE and no Eu anomaly, and 4) 295 ± 6 Ma LREE-depleted rims. We interpret the increase in titanite Y + HREE between ca. 400 and ca. 372 Ma to constrain the timing of diopside fracturing and recrystallization and amphibole breakdown. Apparent Zr-in-titanite temperatures (803 ± 36 °C at 0.5 ± 0.2 GPa) and increased XDi suggest a thermal maximum at ca. 372 Ma. Population 3 domains dated to ca. 342 Ma exhibit no Eu anomaly and are observed only in compositional bands dominated by diopside (> 80 vol %), suggesting limited equilibrium between titanite and plagioclase. Finally, low LREE and high U/Th in Population 4 titanite date the formation of hydrous phases, such as allanite, during high XH2O fluid infiltration at ca. 295 Ma. In contrast to the well-defined date-composition-texture relationships observed for titanite from SSP18-1B, titanite grains from sample SSP18-1A exhibit complex zoning patterns and little correlation between texture, composition, and date. We hypothesize that the incorporation of variable amounts of radiogenic Pb from dissolved titanite into recrystallized domains resulted in mixed ages spanning 380–330 Ma. Although titanite may reliably record multiple phases of metamorphism, these data highlight the importance of considering U-Pb data along with chemical and textural data to screen for inherited radiogenic Pb.

U-Pb age and trace elements composition of titanite from granites of Belokurikhinsky massif, Gorny Altai

As a result of isotope-geochemical study, the age data (U-Pb method, ID-TIMS) of titanite from the first phase granites of the Belokurikhinsky granite massif, Gorny Altai, were obtained for the first time. The concordant value of the titanite age of 255 ± 2 Ma coincides within the margin of error with the previously published results of dating micas from granites of the second and third phases of the Belokurikha massif by the Ar-Ar method (250 ± 3 Ma). At the same time, the results of dating differ significantly from the previously published age values for the granites of the Belokurikha massif (232 ± 5 Ma, U-Pb method for the monofraction of zircon grains; 245 ± 8 Ma, Rb-Sr method for the whole rocks). Therefore, there is every reason to narrow the time interval of the formation of the Belokurikha granite massif to 255-250 Ma. The study of the trace element composition of titanite by SIMS demonstrated their zonal structure. The central part of the titanite grain differs from the rim by a noticeably higher content of REE, Cr, Y, and Nb. The content of V, Zr and Ba decreases to a lesser extent towards the rim, the content of Sr and U remains constant. At the same time, the REE distribution spectra in the central and rim parts are conformal to each other, having a convex spectrum for LREE and a concave one for HREE. Titanite is characterized by a negative Eu-anomaly, the depth of which decreases to the rim of the grain. A negative Eu-anomaly indicates the co-crystallization of titanite and plagioclase. The REE distribution spectra in titanite from the Belokurikha massif correspond to the characteristics of a typical magmatic titanite from granitoids and differ significantly from the distribution spectra in metamorphic titanite.

Zircon U–Pb Dating and Lu-Hf Isotope of the Retrograded Eclogite from Chicheng, Northern Hebei Province, China

We report zircon U–Pb ages and Lu-Hf isotopic data from two sample of the retrograded eclogite in the Chicheng area. Two groups of the metamorphic zircons from the Chicheng retrograded eclogite were identified: group one shows characteristics of depletion in LREE and flat in HREE curves and exhibit no significant Eu anomaly, and this may imply that they may form under eclogite facies metamorphic condition; group two is rich in HREE and shows slight negative Eu anomaly indicated that they may form under amphibolite facies metamorphic condition. Zircon Lu-Hf isotopic of εHf from the Chicheng eclogite has larger span range from 6.0 to 18.0, which suggests that the magma of the eclogite protolith may be mixed with partial crustal components. The peak eclogite facies metamorphism of Chicheng eclogite may occur at 348.5–344.2 Ma and its retrograde metamorphism of amphibolite fancies may occur at ca. 325.0 Ma. The Hongqiyingzi Complex may experience multistage metamorphic events mainly including Late Archean (2494–2448 Ma), Late Paleoproterozoic (1900–1734 Ma, peak age = 1824.6 Ma), and Phanerozoic (495–234 Ma, peak age = 323.7 Ma). Thus, the metamorphic event (348.5–325 Ma) of the Chicheng eclogite is in accordance with the Phanerozoic metamorphic event of the Hongqiyingzi Complex. The eclogite facies metamorphic age of the eclogite is in accordance with the metamorphism (granulite facies or amphibolite facies) of its surrounding rocks, which implied that the tectonic subduction and exhumation of the retrograded eclogite may cause the regional metamorphism of garnet biotite plagioclase gneiss.

Dissolution-Repackaging of Hellandite-(Ce), Mottanaite-(Ce)/Ferri-Mottanaite-(Ce)

We investigated hellandite-group mineral phases from the Roman Region, alkali syenite ejecta, by multimethod analyses. They show a complex crystallisation history including co-precipitation of hellandite-(Ce) with brockite, resorption, sub-solidus substitution with mottanaite-(Ce), exsolution of perthite-like ferri-mottanaite-(Ce), overgrowth of an oscillatory-zoned euhedral shell of ferri-mottanaite-(Ce) and late, secondary precipitation of pyrochlore in the cribrose hellandite-(Ce) core. LREE/HREE crossover and a negative Eu anomaly in hellandite-group minerals follows fO2 increase during magma cooling. The distinction among the hellandite-group minerals is based on the element distribution in the M1, M2, M3, M4 and T sites. Additional information on miscibility relationship among the hellandite sensu strictu, tadzhikite, mottanaite, ferri-mottanaite and ciprianiite endmembers derives from molar fraction calculation. We observed that change in composition of hellandite-group minerals mimic the ligands activity in carbothermal-hydrothermal fluids related to carbonatitic magmatism.

Petrogenesis of the Despen Volcanic Rocks of the Middle–Late Ordovician Volcanoplutonic Association of the Tannu-Ola Terrane (Southwestern Tuva)

––We have studied the structure and composition of a volcanic unit in the valley of the Despen River, on the southern slope of the East Tannu-Ola Ridge. The unit was earlier assigned to the Lower Devonian Kendei Formation. The new geological and geochronological data show that it resulted from explosive volcanism at 460–450 Ma. The Despen volcanic rocks formed in association with granitoids of the Argolik complex at the end of the accretion–collision stage of evolution of the Altai–Sayan region, in particular, the Tannu-Ola terrane. These are predominantly felsic ferroan metaluminous and weakly peraluminous nappe volcanic rocks resulted from the differentiation of tholeiitic basalts. Their REE patterns, like those of the Argolik granitoids, are flat in the HREE, show a distinct Eu anomaly, and suggest magma generation at shallow depths in the upper crust. The magmatic source was of subduction origin, as evidenced by the negative Ta–Nb anomalies in the multielement patterns and by εNd(T) = +3.1 to +5.6, and has a Neoproterozoic model age, TNd(DM-2st) = 0.94–0.69 Ga.

Unusual metasomatites (phyolithites) in the Kolvitskiy gabbro-anorthosite rock mass: composition and structural position

Complex mineralogical, geochemical, and geological-structural characteristics of a rare collection stone of violet color, phyolithite, in the southwestern part of the Kola Peninsula. This is a metasomatic rock formed under the conditions of brittle deformations on gabbro-anorthosites of the Paleoproterozoic Kolvitskiy rock mass. As a result of potassium metasomatosis, the plagioclase of the initial rocks was replaced by a fine-grained mica aggregate of muscovite-phengite composition with inclusions of Va-aluminoseladonite (up to 20-30 microns). Ba-aluminoseladonite contains 6.6-10.5 % by weight of BaO. Manganese is the only chromophore that accumulates in the rock during metasomatosis. It is manganese that provides the purple-violet color of pseudomorphs of mica according to anorthite. The phyolithites is depleted by REE and has a positive Eu-anomaly. The phyolithites are confined to the areas of fracturing of the north-eastern strike, located in the zone of dynamic influence of the north-western closure of the Onega-Kandalaksha rift of the Riphean age. Other formations (injection conglomerates and lamproites) are also associated with the formation of this structure, which owe their origin to an intense fluid flow.

Petrogenesis of a late-stage calc-alkaline granite in a giant S-type batholith: geochronology and Sr–Nd–Pb isotopes from the Nomatsaus granite (Donkerhoek batholith), Namibia

The late-tectonic 511.4 ± 0.6 Ma-old Nomatsaus intrusion (Donkerhoek batholith, Damara orogen, Namibia) consists of moderately peraluminous, magnesian, calc-alkalic to calcic granites similar to I-type granites worldwide. Major and trace-element variations and LREE and HREE concentrations in evolved rocks imply that the fractionated mineral assemblage includes biotite, Fe–Ti oxides, zircon, plagioclase and monazite. Increasing K2O abundance with increasing SiO2 suggests accumulation of K-feldspar; compatible with a small positive Eu anomaly in the most evolved rocks. In comparison with experimental data, the Nomatsaus granite was likely generated from meta-igneous sources of possibly dacitic composition that melted under water-undersaturated conditions (X H2O: 0.25–0.50) and at temperatures between 800 and 850 °C, compatible with the zircon and monazite saturation temperatures of 812 and 852 °C, respectively. The Nomatsaus granite has moderately radiogenic initial 87Sr/86Sr ratios (0.7067–0.7082), relatively radiogenic initial εNd values (− 2.9 to − 4.8) and moderately evolved Pb isotope ratios. Although initial Sr and Nd isotopic compositions of the granite do not vary with SiO2 or MgO contents, fSm/Nd and initial εNd values are negatively correlated indicating limited assimilation of crustal components during monazite-dominated fractional crystallization. The preferred petrogenetic model for the generation of the Nomatsaus granite involves a continent–continent collisional setting with stacking of crustal slices that in combination with high radioactive heat production rates heated the thickened crust, leading to the medium-P/high-T environment characteristic of the southern Central Zone of the Damara orogen. Such a setting promoted partial melting of metasedimentary sources during the initial stages of crustal heating, followed by the partial melting of meta-igneous rocks at mid-crustal levels at higher P–T conditions and relatively late in the orogenic evolution.